The invention is related to a brake pressure control system, in particular for automotive vehicles, with an anti-locking control (ABS) and/or with a traction slip control (TSS), which operates with hydraulic fluid pressure, such systems include a master cylinder, one or more wheel cylinders for wheel brakes, and a pressure modulator for the modulation of the hydraulic pressure within said wheel cylinders of the wheel brakes in the course of a brake pressure control mode These systems also include a motor-driven pump for the generation of hydraulic pressure, and an electronic controller, and an inlet and an outlet valve associated with each wheel cylinder.
An example of such a brake system is described, for example, in the German patent application published without examination, No. 3,731,603. The application of the invention is, however, not limited to this type.
The electronic controller controls operation of the inlet and outlet valves in accordance with the control algorithm incorporated in the controller . A pressure reduction phase is generated in the wheel cylinder when the outlet valve is open and the inlet valve is closed. When the inlet valve is closed and the outlet valve is closed, a pressure stabilization phase is established, and, when the inlet valve is open and the outlet valve is closed a pressure rebuilding-up phase ensues.
Furthermore, hydraulic connections have been described in which the inlet valve has a restriction effect. Please refer to the German patent application No. P 3,919,842.1 in this respect.
In that patent application, a hydraulic brake system for a vehicle is described which is equipped with an anti-locking control system and is comprised of a master cylinder, a fluid pressure accumulator, at least one wheel brake which is in connection with the master brake cylinder through a brake line and is in connection with the fluid pressure accumulator through a return line. An electromagnetically actuated outlet valve is inserted in the return line and shuts off the return line in its normal position and opens the return line in its switching position. A restriction valve is incorporated in the brake line, furnished with two switching positions, an unrestricted connection existing between the wheel brake and the master brake cylinder in the first switching position and a restricted connection existing between the wheel brake and the master brake cylinder in the second switching position. A pump aspirates fluid under pressure from the fluid pressure accumulator and delivers it through a pressure line into the master cylinder. A sensor monitors the angular velocity of the wheel to be braked, and an electronic evaluation unit evaluates the sensor signal and generates switching signals for the pump drive and for the outlet valve.
It is proposed in the forementioned German patent application that the restriction valve is connected by means of a control line to the outlet of the pump so that the pressure at the outlet of the pump puts the restriction valve from the first into the second switching position.
See the above-mentioned German patent application No. P 3,919,842.1 for an illustration of this type of system.
See also U.S. Pat. No. 4,090,739 which describes another such system.
A brake system with anti-locking control is described there which is suited for use in motorcycles or in small automotive vehicles. The system is comprised of an electromagnetically actuatable anti-locking control valve which may assume different positions: a normal position, a pressure decreasing position and a locking position between two pistons. The valve is subject to the action of a spring, urged to the normal position. In that position, the valve communicates brake pressure to the wheel cylinder. In the anti-locking control mode, the valve is slid into the pressure decreasing position. The valve is hindered from returning from the pressure decreasing position into the normal position as long as fluid pressure is exerted by the master cylinder. The valve remains in the locking position when the supply of fluid pressure is locked. A bypass is provided which bridges the control valve. A restricted cross-sectional area of flow is envisaged in the bypass. The objective achieved is that in a second and subsequent pressure build-up phases only a limited volume of brake fluid is made available.
Further details may be seen in the above-mentioned U.S. patent.
The present invention has the following objects:
Basically, the cost of manufacture is to be reduced. This is to be achieved in particular by the saving of magnet coils, of electrical lines and of plug pins.
The assembly space required for the incorporation of the anti-locking control is to be reduced.
The applicability of the inventive anti-locking control is to be more universal than customary according to the state of the art. For example, an application for so-called "open" and "closed" brake systems with anti-locking control is to be possible. Open brake systems are those systems in which a fluid reservoir is vented to the atmosphere and closed systems are systems which do not have an unpressurized reservoir.
The present invention allows the brake passive control to be integrated in the valve block of the control unit.
By the present invention attaining the effect of a flow limiting valve is enabled. This means that after reaching a nominal flow rate, this flow rate is maintained substantially constant notwithstanding fluctuations of the pressure level or pressure differentials up stream and downstream of the valve.
"Nominal flow rate" means in this case that not more than a defined volume of fluid per unit of time is conveyed to the wheel cylinder in the anti-locking control mode, regardless of the level of the pressure on the delivery side of the pump or the pressure side of the master cylinder.
It is, moreover, part of the object of the invention that besides avoiding undesirably high wheel cylinder pressures in the control mode, a rapid pressure reduction takes place in the control mode when a pressure reduction is prescribed by the control algorithm. The control quality is to be improved generally.
The invention has, furthermore, the object to eliminate the electromagnetically actuated inlet valves, open when deenergized, which are typically required in the prior art.
Furthermore, the invention should allow this control independent of any changes of the viscosity and temperature of the fluid. Constant pressure gradients during control should be enabled by the invention.
It is, moreover, one of the objects of the invention to reduce or to prevent any noises during the control mode.
Besides the reduction of the expenditure for electrical lines, also the fittings are reduced in size. In addition, it is to be rendered possible by the invention to reduce the expenditure for the driver stage of the electronic controller. A more simple arrangement of the ducts in the valve assembly for the control as compared to that of the state of the art is to be rendered possible by the invention.